Presently, conditions such as diabetic retinopathy, vein occlusion and age-related macular degeneration have been treated with photocoagulation induced by visible laser light. While this type of visible laser light treatment may halt the progress of the underlying disease, it can be problematic.
One problem is that some ophthalmic treatments require the application of a large number of laser doses to the retina, which can be tedious and time consuming. Such treatments call for the application of each dose in the form of a laser beam spot applied to the target tissue for a predetermined amount of time. The physician is responsible for ensuring that each laser beam spot is properly positioned on the intended target tissue as well as away from sensitive areas of the eye such as the macula that could result in permanent unintended damage. Since some treatments can require hundreds of laser beam spots to treat the target tissues, the overall treatment time can be quite long and require great physician skill to ensure a precise and adequate treatment of the entire target tissue area is accomplished.
To reduce the treatment time needed for retinal photocoagulation, a system and method has been proposed for applying multiple laser spots automatically in the form of a treatment pattern of spots, so that an area of target tissue is efficiently treated by multiple spots pre-positioned on the tissue in the form of the pattern. See for example U.S. Patent Publications 2005/0286019, 2006/0100677 and 2007/0129775. However, rapid delivery of multiple beam spots in patterns raises new issues. For example, the exposure time is limited because of possible eye movement, and even with short exposure times there can be patient eye movement at the moment the physician triggers the application of the treatment pattern that could result in the application of the treatment pattern to non-targeted tissue. Moreover, physicians typically identify the tissue locations to be targeted using pre-treatment images of the eye. Present systems and techniques for applying patterns of spots have no capability of ensuring the tissue targeted for treatment by the physician is the same as that identified in the pre-treatment images. Thus, the physician is solely responsible for ensuring the tissue about to be treated is the same tissue identified in the pre-treatment images, and that the stability of the eye position will allow an accurate application of the treatment pattern. Rapid eye movements called saccades cannot be adequately tracked or compensated for by physicians. Typical physician latency times are approximately 400 ms, and thus physicians usually can only move the laser aiming device at a 5 Hz rate (while eye movements are approximately 100 times faster). Anesthetizing eye muscles using an injection of an anesthetic agent behind the eye can stabilize the eye but carries a risk of perforating the eye, the optic nerve or the blood vessels, is quite painful, and could even cause death.
Accordingly, there is a need for a semi-automated ophthalmic laser treatment and method that compensates for patient eye movement, and/or can assist the physician in verifying and adjusting alignment of the treatment pattern to the target tissue identified in pre-treatment images of the eye.